David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 1 | /* SPDX-License-Identifier: GPL-2.0+ */ |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 2 | /* |
| 3 | * Read-Copy Update mechanism for mutual exclusion |
| 4 | * |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 5 | * Copyright IBM Corporation, 2001 |
| 6 | * |
| 7 | * Author: Dipankar Sarma <dipankar@in.ibm.com> |
| 8 | * |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 9 | * Based on the original work by Paul McKenney <paulmck@vnet.ibm.com> |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 10 | * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. |
| 11 | * Papers: |
| 12 | * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf |
| 13 | * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) |
| 14 | * |
| 15 | * For detailed explanation of Read-Copy Update mechanism see - |
| 16 | * http://lse.sourceforge.net/locking/rcupdate.html |
| 17 | * |
| 18 | */ |
| 19 | |
| 20 | #ifndef __LINUX_RCUPDATE_H |
| 21 | #define __LINUX_RCUPDATE_H |
| 22 | |
| 23 | #include <linux/types.h> |
| 24 | #include <linux/compiler.h> |
| 25 | #include <linux/atomic.h> |
| 26 | #include <linux/irqflags.h> |
| 27 | #include <linux/preempt.h> |
| 28 | #include <linux/bottom_half.h> |
| 29 | #include <linux/lockdep.h> |
| 30 | #include <asm/processor.h> |
| 31 | #include <linux/cpumask.h> |
| 32 | |
| 33 | #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) |
| 34 | #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) |
| 35 | #define ulong2long(a) (*(long *)(&(a))) |
| 36 | |
| 37 | /* Exported common interfaces */ |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 38 | void call_rcu(struct rcu_head *head, rcu_callback_t func); |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 39 | void rcu_barrier_tasks(void); |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 40 | void synchronize_rcu(void); |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 41 | |
| 42 | #ifdef CONFIG_PREEMPT_RCU |
| 43 | |
| 44 | void __rcu_read_lock(void); |
| 45 | void __rcu_read_unlock(void); |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 46 | |
| 47 | /* |
| 48 | * Defined as a macro as it is a very low level header included from |
| 49 | * areas that don't even know about current. This gives the rcu_read_lock() |
| 50 | * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other |
| 51 | * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. |
| 52 | */ |
| 53 | #define rcu_preempt_depth() (current->rcu_read_lock_nesting) |
| 54 | |
| 55 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
| 56 | |
| 57 | static inline void __rcu_read_lock(void) |
| 58 | { |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 59 | preempt_disable(); |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 60 | } |
| 61 | |
| 62 | static inline void __rcu_read_unlock(void) |
| 63 | { |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 64 | preempt_enable(); |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 65 | } |
| 66 | |
| 67 | static inline int rcu_preempt_depth(void) |
| 68 | { |
| 69 | return 0; |
| 70 | } |
| 71 | |
| 72 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ |
| 73 | |
| 74 | /* Internal to kernel */ |
| 75 | void rcu_init(void); |
| 76 | extern int rcu_scheduler_active __read_mostly; |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 77 | void rcu_sched_clock_irq(int user); |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 78 | void rcu_report_dead(unsigned int cpu); |
| 79 | void rcutree_migrate_callbacks(int cpu); |
| 80 | |
| 81 | #ifdef CONFIG_RCU_STALL_COMMON |
| 82 | void rcu_sysrq_start(void); |
| 83 | void rcu_sysrq_end(void); |
| 84 | #else /* #ifdef CONFIG_RCU_STALL_COMMON */ |
| 85 | static inline void rcu_sysrq_start(void) { } |
| 86 | static inline void rcu_sysrq_end(void) { } |
| 87 | #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */ |
| 88 | |
| 89 | #ifdef CONFIG_NO_HZ_FULL |
| 90 | void rcu_user_enter(void); |
| 91 | void rcu_user_exit(void); |
| 92 | #else |
| 93 | static inline void rcu_user_enter(void) { } |
| 94 | static inline void rcu_user_exit(void) { } |
| 95 | #endif /* CONFIG_NO_HZ_FULL */ |
| 96 | |
| 97 | #ifdef CONFIG_RCU_NOCB_CPU |
| 98 | void rcu_init_nohz(void); |
| 99 | #else /* #ifdef CONFIG_RCU_NOCB_CPU */ |
| 100 | static inline void rcu_init_nohz(void) { } |
| 101 | #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ |
| 102 | |
| 103 | /** |
| 104 | * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers |
| 105 | * @a: Code that RCU needs to pay attention to. |
| 106 | * |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 107 | * RCU read-side critical sections are forbidden in the inner idle loop, |
| 108 | * that is, between the rcu_idle_enter() and the rcu_idle_exit() -- RCU |
| 109 | * will happily ignore any such read-side critical sections. However, |
| 110 | * things like powertop need tracepoints in the inner idle loop. |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 111 | * |
| 112 | * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU()) |
| 113 | * will tell RCU that it needs to pay attention, invoke its argument |
| 114 | * (in this example, calling the do_something_with_RCU() function), |
| 115 | * and then tell RCU to go back to ignoring this CPU. It is permissible |
| 116 | * to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is |
| 117 | * on the order of a million or so, even on 32-bit systems). It is |
| 118 | * not legal to block within RCU_NONIDLE(), nor is it permissible to |
| 119 | * transfer control either into or out of RCU_NONIDLE()'s statement. |
| 120 | */ |
| 121 | #define RCU_NONIDLE(a) \ |
| 122 | do { \ |
| 123 | rcu_irq_enter_irqson(); \ |
| 124 | do { a; } while (0); \ |
| 125 | rcu_irq_exit_irqson(); \ |
| 126 | } while (0) |
| 127 | |
| 128 | /* |
| 129 | * Note a quasi-voluntary context switch for RCU-tasks's benefit. |
| 130 | * This is a macro rather than an inline function to avoid #include hell. |
| 131 | */ |
| 132 | #ifdef CONFIG_TASKS_RCU |
| 133 | #define rcu_tasks_qs(t) \ |
| 134 | do { \ |
| 135 | if (READ_ONCE((t)->rcu_tasks_holdout)) \ |
| 136 | WRITE_ONCE((t)->rcu_tasks_holdout, false); \ |
| 137 | } while (0) |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 138 | #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t) |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 139 | void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); |
| 140 | void synchronize_rcu_tasks(void); |
| 141 | void exit_tasks_rcu_start(void); |
| 142 | void exit_tasks_rcu_finish(void); |
| 143 | #else /* #ifdef CONFIG_TASKS_RCU */ |
| 144 | #define rcu_tasks_qs(t) do { } while (0) |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 145 | #define rcu_note_voluntary_context_switch(t) do { } while (0) |
| 146 | #define call_rcu_tasks call_rcu |
| 147 | #define synchronize_rcu_tasks synchronize_rcu |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 148 | static inline void exit_tasks_rcu_start(void) { } |
| 149 | static inline void exit_tasks_rcu_finish(void) { } |
| 150 | #endif /* #else #ifdef CONFIG_TASKS_RCU */ |
| 151 | |
| 152 | /** |
| 153 | * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU |
| 154 | * |
| 155 | * This macro resembles cond_resched(), except that it is defined to |
| 156 | * report potential quiescent states to RCU-tasks even if the cond_resched() |
| 157 | * machinery were to be shut off, as some advocate for PREEMPT kernels. |
| 158 | */ |
| 159 | #define cond_resched_tasks_rcu_qs() \ |
| 160 | do { \ |
| 161 | rcu_tasks_qs(current); \ |
| 162 | cond_resched(); \ |
| 163 | } while (0) |
| 164 | |
| 165 | /* |
| 166 | * Infrastructure to implement the synchronize_() primitives in |
| 167 | * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. |
| 168 | */ |
| 169 | |
| 170 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU) |
| 171 | #include <linux/rcutree.h> |
| 172 | #elif defined(CONFIG_TINY_RCU) |
| 173 | #include <linux/rcutiny.h> |
| 174 | #else |
| 175 | #error "Unknown RCU implementation specified to kernel configuration" |
| 176 | #endif |
| 177 | |
| 178 | /* |
| 179 | * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls |
| 180 | * are needed for dynamic initialization and destruction of rcu_head |
| 181 | * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for |
| 182 | * dynamic initialization and destruction of statically allocated rcu_head |
| 183 | * structures. However, rcu_head structures allocated dynamically in the |
| 184 | * heap don't need any initialization. |
| 185 | */ |
| 186 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD |
| 187 | void init_rcu_head(struct rcu_head *head); |
| 188 | void destroy_rcu_head(struct rcu_head *head); |
| 189 | void init_rcu_head_on_stack(struct rcu_head *head); |
| 190 | void destroy_rcu_head_on_stack(struct rcu_head *head); |
| 191 | #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
| 192 | static inline void init_rcu_head(struct rcu_head *head) { } |
| 193 | static inline void destroy_rcu_head(struct rcu_head *head) { } |
| 194 | static inline void init_rcu_head_on_stack(struct rcu_head *head) { } |
| 195 | static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { } |
| 196 | #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
| 197 | |
| 198 | #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) |
| 199 | bool rcu_lockdep_current_cpu_online(void); |
| 200 | #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ |
| 201 | static inline bool rcu_lockdep_current_cpu_online(void) { return true; } |
| 202 | #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ |
| 203 | |
| 204 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
| 205 | |
| 206 | static inline void rcu_lock_acquire(struct lockdep_map *map) |
| 207 | { |
| 208 | lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_); |
| 209 | } |
| 210 | |
| 211 | static inline void rcu_lock_release(struct lockdep_map *map) |
| 212 | { |
| 213 | lock_release(map, 1, _THIS_IP_); |
| 214 | } |
| 215 | |
| 216 | extern struct lockdep_map rcu_lock_map; |
| 217 | extern struct lockdep_map rcu_bh_lock_map; |
| 218 | extern struct lockdep_map rcu_sched_lock_map; |
| 219 | extern struct lockdep_map rcu_callback_map; |
| 220 | int debug_lockdep_rcu_enabled(void); |
| 221 | int rcu_read_lock_held(void); |
| 222 | int rcu_read_lock_bh_held(void); |
| 223 | int rcu_read_lock_sched_held(void); |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 224 | int rcu_read_lock_any_held(void); |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 225 | |
| 226 | #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
| 227 | |
| 228 | # define rcu_lock_acquire(a) do { } while (0) |
| 229 | # define rcu_lock_release(a) do { } while (0) |
| 230 | |
| 231 | static inline int rcu_read_lock_held(void) |
| 232 | { |
| 233 | return 1; |
| 234 | } |
| 235 | |
| 236 | static inline int rcu_read_lock_bh_held(void) |
| 237 | { |
| 238 | return 1; |
| 239 | } |
| 240 | |
| 241 | static inline int rcu_read_lock_sched_held(void) |
| 242 | { |
| 243 | return !preemptible(); |
| 244 | } |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 245 | |
| 246 | static inline int rcu_read_lock_any_held(void) |
| 247 | { |
| 248 | return !preemptible(); |
| 249 | } |
| 250 | |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 251 | #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
| 252 | |
| 253 | #ifdef CONFIG_PROVE_RCU |
| 254 | |
| 255 | /** |
| 256 | * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met |
| 257 | * @c: condition to check |
| 258 | * @s: informative message |
| 259 | */ |
| 260 | #define RCU_LOCKDEP_WARN(c, s) \ |
| 261 | do { \ |
| 262 | static bool __section(.data.unlikely) __warned; \ |
| 263 | if (debug_lockdep_rcu_enabled() && !__warned && (c)) { \ |
| 264 | __warned = true; \ |
| 265 | lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ |
| 266 | } \ |
| 267 | } while (0) |
| 268 | |
| 269 | #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU) |
| 270 | static inline void rcu_preempt_sleep_check(void) |
| 271 | { |
| 272 | RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map), |
| 273 | "Illegal context switch in RCU read-side critical section"); |
| 274 | } |
| 275 | #else /* #ifdef CONFIG_PROVE_RCU */ |
| 276 | static inline void rcu_preempt_sleep_check(void) { } |
| 277 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ |
| 278 | |
| 279 | #define rcu_sleep_check() \ |
| 280 | do { \ |
| 281 | rcu_preempt_sleep_check(); \ |
| 282 | RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \ |
| 283 | "Illegal context switch in RCU-bh read-side critical section"); \ |
| 284 | RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \ |
| 285 | "Illegal context switch in RCU-sched read-side critical section"); \ |
| 286 | } while (0) |
| 287 | |
| 288 | #else /* #ifdef CONFIG_PROVE_RCU */ |
| 289 | |
| 290 | #define RCU_LOCKDEP_WARN(c, s) do { } while (0) |
| 291 | #define rcu_sleep_check() do { } while (0) |
| 292 | |
| 293 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ |
| 294 | |
| 295 | /* |
| 296 | * Helper functions for rcu_dereference_check(), rcu_dereference_protected() |
| 297 | * and rcu_assign_pointer(). Some of these could be folded into their |
| 298 | * callers, but they are left separate in order to ease introduction of |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 299 | * multiple pointers markings to match different RCU implementations |
| 300 | * (e.g., __srcu), should this make sense in the future. |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 301 | */ |
| 302 | |
| 303 | #ifdef __CHECKER__ |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 304 | #define rcu_check_sparse(p, space) \ |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 305 | ((void)(((typeof(*p) space *)p) == p)) |
| 306 | #else /* #ifdef __CHECKER__ */ |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 307 | #define rcu_check_sparse(p, space) |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 308 | #endif /* #else #ifdef __CHECKER__ */ |
| 309 | |
| 310 | #define __rcu_access_pointer(p, space) \ |
| 311 | ({ \ |
| 312 | typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \ |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 313 | rcu_check_sparse(p, space); \ |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 314 | ((typeof(*p) __force __kernel *)(_________p1)); \ |
| 315 | }) |
| 316 | #define __rcu_dereference_check(p, c, space) \ |
| 317 | ({ \ |
| 318 | /* Dependency order vs. p above. */ \ |
| 319 | typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \ |
| 320 | RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \ |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 321 | rcu_check_sparse(p, space); \ |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 322 | ((typeof(*p) __force __kernel *)(________p1)); \ |
| 323 | }) |
| 324 | #define __rcu_dereference_protected(p, c, space) \ |
| 325 | ({ \ |
| 326 | RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \ |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 327 | rcu_check_sparse(p, space); \ |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 328 | ((typeof(*p) __force __kernel *)(p)); \ |
| 329 | }) |
| 330 | #define rcu_dereference_raw(p) \ |
| 331 | ({ \ |
| 332 | /* Dependency order vs. p above. */ \ |
| 333 | typeof(p) ________p1 = READ_ONCE(p); \ |
| 334 | ((typeof(*p) __force __kernel *)(________p1)); \ |
| 335 | }) |
| 336 | |
| 337 | /** |
| 338 | * RCU_INITIALIZER() - statically initialize an RCU-protected global variable |
| 339 | * @v: The value to statically initialize with. |
| 340 | */ |
| 341 | #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v) |
| 342 | |
| 343 | /** |
| 344 | * rcu_assign_pointer() - assign to RCU-protected pointer |
| 345 | * @p: pointer to assign to |
| 346 | * @v: value to assign (publish) |
| 347 | * |
| 348 | * Assigns the specified value to the specified RCU-protected |
| 349 | * pointer, ensuring that any concurrent RCU readers will see |
| 350 | * any prior initialization. |
| 351 | * |
| 352 | * Inserts memory barriers on architectures that require them |
| 353 | * (which is most of them), and also prevents the compiler from |
| 354 | * reordering the code that initializes the structure after the pointer |
| 355 | * assignment. More importantly, this call documents which pointers |
| 356 | * will be dereferenced by RCU read-side code. |
| 357 | * |
| 358 | * In some special cases, you may use RCU_INIT_POINTER() instead |
| 359 | * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due |
| 360 | * to the fact that it does not constrain either the CPU or the compiler. |
| 361 | * That said, using RCU_INIT_POINTER() when you should have used |
| 362 | * rcu_assign_pointer() is a very bad thing that results in |
| 363 | * impossible-to-diagnose memory corruption. So please be careful. |
| 364 | * See the RCU_INIT_POINTER() comment header for details. |
| 365 | * |
| 366 | * Note that rcu_assign_pointer() evaluates each of its arguments only |
| 367 | * once, appearances notwithstanding. One of the "extra" evaluations |
| 368 | * is in typeof() and the other visible only to sparse (__CHECKER__), |
| 369 | * neither of which actually execute the argument. As with most cpp |
| 370 | * macros, this execute-arguments-only-once property is important, so |
| 371 | * please be careful when making changes to rcu_assign_pointer() and the |
| 372 | * other macros that it invokes. |
| 373 | */ |
| 374 | #define rcu_assign_pointer(p, v) \ |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 375 | do { \ |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 376 | uintptr_t _r_a_p__v = (uintptr_t)(v); \ |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 377 | rcu_check_sparse(p, __rcu); \ |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 378 | \ |
| 379 | if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \ |
| 380 | WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \ |
| 381 | else \ |
| 382 | smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \ |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 383 | } while (0) |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 384 | |
| 385 | /** |
| 386 | * rcu_swap_protected() - swap an RCU and a regular pointer |
| 387 | * @rcu_ptr: RCU pointer |
| 388 | * @ptr: regular pointer |
| 389 | * @c: the conditions under which the dereference will take place |
| 390 | * |
| 391 | * Perform swap(@rcu_ptr, @ptr) where @rcu_ptr is an RCU-annotated pointer and |
| 392 | * @c is the argument that is passed to the rcu_dereference_protected() call |
| 393 | * used to read that pointer. |
| 394 | */ |
| 395 | #define rcu_swap_protected(rcu_ptr, ptr, c) do { \ |
| 396 | typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \ |
| 397 | rcu_assign_pointer((rcu_ptr), (ptr)); \ |
| 398 | (ptr) = __tmp; \ |
| 399 | } while (0) |
| 400 | |
| 401 | /** |
| 402 | * rcu_access_pointer() - fetch RCU pointer with no dereferencing |
| 403 | * @p: The pointer to read |
| 404 | * |
| 405 | * Return the value of the specified RCU-protected pointer, but omit the |
| 406 | * lockdep checks for being in an RCU read-side critical section. This is |
| 407 | * useful when the value of this pointer is accessed, but the pointer is |
| 408 | * not dereferenced, for example, when testing an RCU-protected pointer |
| 409 | * against NULL. Although rcu_access_pointer() may also be used in cases |
| 410 | * where update-side locks prevent the value of the pointer from changing, |
| 411 | * you should instead use rcu_dereference_protected() for this use case. |
| 412 | * |
| 413 | * It is also permissible to use rcu_access_pointer() when read-side |
| 414 | * access to the pointer was removed at least one grace period ago, as |
| 415 | * is the case in the context of the RCU callback that is freeing up |
| 416 | * the data, or after a synchronize_rcu() returns. This can be useful |
| 417 | * when tearing down multi-linked structures after a grace period |
| 418 | * has elapsed. |
| 419 | */ |
| 420 | #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) |
| 421 | |
| 422 | /** |
| 423 | * rcu_dereference_check() - rcu_dereference with debug checking |
| 424 | * @p: The pointer to read, prior to dereferencing |
| 425 | * @c: The conditions under which the dereference will take place |
| 426 | * |
| 427 | * Do an rcu_dereference(), but check that the conditions under which the |
| 428 | * dereference will take place are correct. Typically the conditions |
| 429 | * indicate the various locking conditions that should be held at that |
| 430 | * point. The check should return true if the conditions are satisfied. |
| 431 | * An implicit check for being in an RCU read-side critical section |
| 432 | * (rcu_read_lock()) is included. |
| 433 | * |
| 434 | * For example: |
| 435 | * |
| 436 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); |
| 437 | * |
| 438 | * could be used to indicate to lockdep that foo->bar may only be dereferenced |
| 439 | * if either rcu_read_lock() is held, or that the lock required to replace |
| 440 | * the bar struct at foo->bar is held. |
| 441 | * |
| 442 | * Note that the list of conditions may also include indications of when a lock |
| 443 | * need not be held, for example during initialisation or destruction of the |
| 444 | * target struct: |
| 445 | * |
| 446 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || |
| 447 | * atomic_read(&foo->usage) == 0); |
| 448 | * |
| 449 | * Inserts memory barriers on architectures that require them |
| 450 | * (currently only the Alpha), prevents the compiler from refetching |
| 451 | * (and from merging fetches), and, more importantly, documents exactly |
| 452 | * which pointers are protected by RCU and checks that the pointer is |
| 453 | * annotated as __rcu. |
| 454 | */ |
| 455 | #define rcu_dereference_check(p, c) \ |
| 456 | __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu) |
| 457 | |
| 458 | /** |
| 459 | * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking |
| 460 | * @p: The pointer to read, prior to dereferencing |
| 461 | * @c: The conditions under which the dereference will take place |
| 462 | * |
| 463 | * This is the RCU-bh counterpart to rcu_dereference_check(). |
| 464 | */ |
| 465 | #define rcu_dereference_bh_check(p, c) \ |
| 466 | __rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu) |
| 467 | |
| 468 | /** |
| 469 | * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking |
| 470 | * @p: The pointer to read, prior to dereferencing |
| 471 | * @c: The conditions under which the dereference will take place |
| 472 | * |
| 473 | * This is the RCU-sched counterpart to rcu_dereference_check(). |
| 474 | */ |
| 475 | #define rcu_dereference_sched_check(p, c) \ |
| 476 | __rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \ |
| 477 | __rcu) |
| 478 | |
| 479 | /* |
| 480 | * The tracing infrastructure traces RCU (we want that), but unfortunately |
| 481 | * some of the RCU checks causes tracing to lock up the system. |
| 482 | * |
| 483 | * The no-tracing version of rcu_dereference_raw() must not call |
| 484 | * rcu_read_lock_held(). |
| 485 | */ |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 486 | #define rcu_dereference_raw_check(p) __rcu_dereference_check((p), 1, __rcu) |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 487 | |
| 488 | /** |
| 489 | * rcu_dereference_protected() - fetch RCU pointer when updates prevented |
| 490 | * @p: The pointer to read, prior to dereferencing |
| 491 | * @c: The conditions under which the dereference will take place |
| 492 | * |
| 493 | * Return the value of the specified RCU-protected pointer, but omit |
| 494 | * the READ_ONCE(). This is useful in cases where update-side locks |
| 495 | * prevent the value of the pointer from changing. Please note that this |
| 496 | * primitive does *not* prevent the compiler from repeating this reference |
| 497 | * or combining it with other references, so it should not be used without |
| 498 | * protection of appropriate locks. |
| 499 | * |
| 500 | * This function is only for update-side use. Using this function |
| 501 | * when protected only by rcu_read_lock() will result in infrequent |
| 502 | * but very ugly failures. |
| 503 | */ |
| 504 | #define rcu_dereference_protected(p, c) \ |
| 505 | __rcu_dereference_protected((p), (c), __rcu) |
| 506 | |
| 507 | |
| 508 | /** |
| 509 | * rcu_dereference() - fetch RCU-protected pointer for dereferencing |
| 510 | * @p: The pointer to read, prior to dereferencing |
| 511 | * |
| 512 | * This is a simple wrapper around rcu_dereference_check(). |
| 513 | */ |
| 514 | #define rcu_dereference(p) rcu_dereference_check(p, 0) |
| 515 | |
| 516 | /** |
| 517 | * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing |
| 518 | * @p: The pointer to read, prior to dereferencing |
| 519 | * |
| 520 | * Makes rcu_dereference_check() do the dirty work. |
| 521 | */ |
| 522 | #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) |
| 523 | |
| 524 | /** |
| 525 | * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing |
| 526 | * @p: The pointer to read, prior to dereferencing |
| 527 | * |
| 528 | * Makes rcu_dereference_check() do the dirty work. |
| 529 | */ |
| 530 | #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) |
| 531 | |
| 532 | /** |
| 533 | * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism |
| 534 | * @p: The pointer to hand off |
| 535 | * |
| 536 | * This is simply an identity function, but it documents where a pointer |
| 537 | * is handed off from RCU to some other synchronization mechanism, for |
| 538 | * example, reference counting or locking. In C11, it would map to |
| 539 | * kill_dependency(). It could be used as follows:: |
| 540 | * |
| 541 | * rcu_read_lock(); |
| 542 | * p = rcu_dereference(gp); |
| 543 | * long_lived = is_long_lived(p); |
| 544 | * if (long_lived) { |
| 545 | * if (!atomic_inc_not_zero(p->refcnt)) |
| 546 | * long_lived = false; |
| 547 | * else |
| 548 | * p = rcu_pointer_handoff(p); |
| 549 | * } |
| 550 | * rcu_read_unlock(); |
| 551 | */ |
| 552 | #define rcu_pointer_handoff(p) (p) |
| 553 | |
| 554 | /** |
| 555 | * rcu_read_lock() - mark the beginning of an RCU read-side critical section |
| 556 | * |
| 557 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
| 558 | * are within RCU read-side critical sections, then the |
| 559 | * synchronize_rcu() is guaranteed to block until after all the other |
| 560 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
| 561 | * on one CPU while other CPUs are within RCU read-side critical |
| 562 | * sections, invocation of the corresponding RCU callback is deferred |
| 563 | * until after the all the other CPUs exit their critical sections. |
| 564 | * |
| 565 | * Note, however, that RCU callbacks are permitted to run concurrently |
| 566 | * with new RCU read-side critical sections. One way that this can happen |
| 567 | * is via the following sequence of events: (1) CPU 0 enters an RCU |
| 568 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register |
| 569 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, |
| 570 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU |
| 571 | * callback is invoked. This is legal, because the RCU read-side critical |
| 572 | * section that was running concurrently with the call_rcu() (and which |
| 573 | * therefore might be referencing something that the corresponding RCU |
| 574 | * callback would free up) has completed before the corresponding |
| 575 | * RCU callback is invoked. |
| 576 | * |
| 577 | * RCU read-side critical sections may be nested. Any deferred actions |
| 578 | * will be deferred until the outermost RCU read-side critical section |
| 579 | * completes. |
| 580 | * |
| 581 | * You can avoid reading and understanding the next paragraph by |
| 582 | * following this rule: don't put anything in an rcu_read_lock() RCU |
| 583 | * read-side critical section that would block in a !PREEMPT kernel. |
| 584 | * But if you want the full story, read on! |
| 585 | * |
| 586 | * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), |
| 587 | * it is illegal to block while in an RCU read-side critical section. |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 588 | * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 589 | * kernel builds, RCU read-side critical sections may be preempted, |
| 590 | * but explicit blocking is illegal. Finally, in preemptible RCU |
| 591 | * implementations in real-time (with -rt patchset) kernel builds, RCU |
| 592 | * read-side critical sections may be preempted and they may also block, but |
| 593 | * only when acquiring spinlocks that are subject to priority inheritance. |
| 594 | */ |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 595 | static __always_inline void rcu_read_lock(void) |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 596 | { |
| 597 | __rcu_read_lock(); |
| 598 | __acquire(RCU); |
| 599 | rcu_lock_acquire(&rcu_lock_map); |
| 600 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
| 601 | "rcu_read_lock() used illegally while idle"); |
| 602 | } |
| 603 | |
| 604 | /* |
| 605 | * So where is rcu_write_lock()? It does not exist, as there is no |
| 606 | * way for writers to lock out RCU readers. This is a feature, not |
| 607 | * a bug -- this property is what provides RCU's performance benefits. |
| 608 | * Of course, writers must coordinate with each other. The normal |
| 609 | * spinlock primitives work well for this, but any other technique may be |
| 610 | * used as well. RCU does not care how the writers keep out of each |
| 611 | * others' way, as long as they do so. |
| 612 | */ |
| 613 | |
| 614 | /** |
| 615 | * rcu_read_unlock() - marks the end of an RCU read-side critical section. |
| 616 | * |
| 617 | * In most situations, rcu_read_unlock() is immune from deadlock. |
| 618 | * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock() |
| 619 | * is responsible for deboosting, which it does via rt_mutex_unlock(). |
| 620 | * Unfortunately, this function acquires the scheduler's runqueue and |
| 621 | * priority-inheritance spinlocks. This means that deadlock could result |
| 622 | * if the caller of rcu_read_unlock() already holds one of these locks or |
| 623 | * any lock that is ever acquired while holding them. |
| 624 | * |
| 625 | * That said, RCU readers are never priority boosted unless they were |
| 626 | * preempted. Therefore, one way to avoid deadlock is to make sure |
| 627 | * that preemption never happens within any RCU read-side critical |
| 628 | * section whose outermost rcu_read_unlock() is called with one of |
| 629 | * rt_mutex_unlock()'s locks held. Such preemption can be avoided in |
| 630 | * a number of ways, for example, by invoking preempt_disable() before |
| 631 | * critical section's outermost rcu_read_lock(). |
| 632 | * |
| 633 | * Given that the set of locks acquired by rt_mutex_unlock() might change |
| 634 | * at any time, a somewhat more future-proofed approach is to make sure |
| 635 | * that that preemption never happens within any RCU read-side critical |
| 636 | * section whose outermost rcu_read_unlock() is called with irqs disabled. |
| 637 | * This approach relies on the fact that rt_mutex_unlock() currently only |
| 638 | * acquires irq-disabled locks. |
| 639 | * |
| 640 | * The second of these two approaches is best in most situations, |
| 641 | * however, the first approach can also be useful, at least to those |
| 642 | * developers willing to keep abreast of the set of locks acquired by |
| 643 | * rt_mutex_unlock(). |
| 644 | * |
| 645 | * See rcu_read_lock() for more information. |
| 646 | */ |
| 647 | static inline void rcu_read_unlock(void) |
| 648 | { |
| 649 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
| 650 | "rcu_read_unlock() used illegally while idle"); |
| 651 | __release(RCU); |
| 652 | __rcu_read_unlock(); |
| 653 | rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */ |
| 654 | } |
| 655 | |
| 656 | /** |
| 657 | * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section |
| 658 | * |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 659 | * This is equivalent of rcu_read_lock(), but also disables softirqs. |
| 660 | * Note that anything else that disables softirqs can also serve as |
| 661 | * an RCU read-side critical section. |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 662 | * |
| 663 | * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh() |
| 664 | * must occur in the same context, for example, it is illegal to invoke |
| 665 | * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh() |
| 666 | * was invoked from some other task. |
| 667 | */ |
| 668 | static inline void rcu_read_lock_bh(void) |
| 669 | { |
| 670 | local_bh_disable(); |
| 671 | __acquire(RCU_BH); |
| 672 | rcu_lock_acquire(&rcu_bh_lock_map); |
| 673 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
| 674 | "rcu_read_lock_bh() used illegally while idle"); |
| 675 | } |
| 676 | |
| 677 | /* |
| 678 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section |
| 679 | * |
| 680 | * See rcu_read_lock_bh() for more information. |
| 681 | */ |
| 682 | static inline void rcu_read_unlock_bh(void) |
| 683 | { |
| 684 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
| 685 | "rcu_read_unlock_bh() used illegally while idle"); |
| 686 | rcu_lock_release(&rcu_bh_lock_map); |
| 687 | __release(RCU_BH); |
| 688 | local_bh_enable(); |
| 689 | } |
| 690 | |
| 691 | /** |
| 692 | * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section |
| 693 | * |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 694 | * This is equivalent of rcu_read_lock(), but disables preemption. |
| 695 | * Read-side critical sections can also be introduced by anything else |
| 696 | * that disables preemption, including local_irq_disable() and friends. |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 697 | * |
| 698 | * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched() |
| 699 | * must occur in the same context, for example, it is illegal to invoke |
| 700 | * rcu_read_unlock_sched() from process context if the matching |
| 701 | * rcu_read_lock_sched() was invoked from an NMI handler. |
| 702 | */ |
| 703 | static inline void rcu_read_lock_sched(void) |
| 704 | { |
| 705 | preempt_disable(); |
| 706 | __acquire(RCU_SCHED); |
| 707 | rcu_lock_acquire(&rcu_sched_lock_map); |
| 708 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
| 709 | "rcu_read_lock_sched() used illegally while idle"); |
| 710 | } |
| 711 | |
| 712 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ |
| 713 | static inline notrace void rcu_read_lock_sched_notrace(void) |
| 714 | { |
| 715 | preempt_disable_notrace(); |
| 716 | __acquire(RCU_SCHED); |
| 717 | } |
| 718 | |
| 719 | /* |
| 720 | * rcu_read_unlock_sched - marks the end of a RCU-classic critical section |
| 721 | * |
| 722 | * See rcu_read_lock_sched for more information. |
| 723 | */ |
| 724 | static inline void rcu_read_unlock_sched(void) |
| 725 | { |
| 726 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
| 727 | "rcu_read_unlock_sched() used illegally while idle"); |
| 728 | rcu_lock_release(&rcu_sched_lock_map); |
| 729 | __release(RCU_SCHED); |
| 730 | preempt_enable(); |
| 731 | } |
| 732 | |
| 733 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ |
| 734 | static inline notrace void rcu_read_unlock_sched_notrace(void) |
| 735 | { |
| 736 | __release(RCU_SCHED); |
| 737 | preempt_enable_notrace(); |
| 738 | } |
| 739 | |
| 740 | /** |
| 741 | * RCU_INIT_POINTER() - initialize an RCU protected pointer |
| 742 | * @p: The pointer to be initialized. |
| 743 | * @v: The value to initialized the pointer to. |
| 744 | * |
| 745 | * Initialize an RCU-protected pointer in special cases where readers |
| 746 | * do not need ordering constraints on the CPU or the compiler. These |
| 747 | * special cases are: |
| 748 | * |
| 749 | * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer *or* |
| 750 | * 2. The caller has taken whatever steps are required to prevent |
| 751 | * RCU readers from concurrently accessing this pointer *or* |
| 752 | * 3. The referenced data structure has already been exposed to |
| 753 | * readers either at compile time or via rcu_assign_pointer() *and* |
| 754 | * |
| 755 | * a. You have not made *any* reader-visible changes to |
| 756 | * this structure since then *or* |
| 757 | * b. It is OK for readers accessing this structure from its |
| 758 | * new location to see the old state of the structure. (For |
| 759 | * example, the changes were to statistical counters or to |
| 760 | * other state where exact synchronization is not required.) |
| 761 | * |
| 762 | * Failure to follow these rules governing use of RCU_INIT_POINTER() will |
| 763 | * result in impossible-to-diagnose memory corruption. As in the structures |
| 764 | * will look OK in crash dumps, but any concurrent RCU readers might |
| 765 | * see pre-initialized values of the referenced data structure. So |
| 766 | * please be very careful how you use RCU_INIT_POINTER()!!! |
| 767 | * |
| 768 | * If you are creating an RCU-protected linked structure that is accessed |
| 769 | * by a single external-to-structure RCU-protected pointer, then you may |
| 770 | * use RCU_INIT_POINTER() to initialize the internal RCU-protected |
| 771 | * pointers, but you must use rcu_assign_pointer() to initialize the |
| 772 | * external-to-structure pointer *after* you have completely initialized |
| 773 | * the reader-accessible portions of the linked structure. |
| 774 | * |
| 775 | * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no |
| 776 | * ordering guarantees for either the CPU or the compiler. |
| 777 | */ |
| 778 | #define RCU_INIT_POINTER(p, v) \ |
| 779 | do { \ |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 780 | rcu_check_sparse(p, __rcu); \ |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 781 | WRITE_ONCE(p, RCU_INITIALIZER(v)); \ |
| 782 | } while (0) |
| 783 | |
| 784 | /** |
| 785 | * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer |
| 786 | * @p: The pointer to be initialized. |
| 787 | * @v: The value to initialized the pointer to. |
| 788 | * |
| 789 | * GCC-style initialization for an RCU-protected pointer in a structure field. |
| 790 | */ |
| 791 | #define RCU_POINTER_INITIALIZER(p, v) \ |
| 792 | .p = RCU_INITIALIZER(v) |
| 793 | |
| 794 | /* |
| 795 | * Does the specified offset indicate that the corresponding rcu_head |
| 796 | * structure can be handled by kfree_rcu()? |
| 797 | */ |
| 798 | #define __is_kfree_rcu_offset(offset) ((offset) < 4096) |
| 799 | |
| 800 | /* |
| 801 | * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain. |
| 802 | */ |
| 803 | #define __kfree_rcu(head, offset) \ |
| 804 | do { \ |
| 805 | BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \ |
| 806 | kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \ |
| 807 | } while (0) |
| 808 | |
| 809 | /** |
| 810 | * kfree_rcu() - kfree an object after a grace period. |
| 811 | * @ptr: pointer to kfree |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 812 | * @rhf: the name of the struct rcu_head within the type of @ptr. |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 813 | * |
| 814 | * Many rcu callbacks functions just call kfree() on the base structure. |
| 815 | * These functions are trivial, but their size adds up, and furthermore |
| 816 | * when they are used in a kernel module, that module must invoke the |
| 817 | * high-latency rcu_barrier() function at module-unload time. |
| 818 | * |
| 819 | * The kfree_rcu() function handles this issue. Rather than encoding a |
| 820 | * function address in the embedded rcu_head structure, kfree_rcu() instead |
| 821 | * encodes the offset of the rcu_head structure within the base structure. |
| 822 | * Because the functions are not allowed in the low-order 4096 bytes of |
| 823 | * kernel virtual memory, offsets up to 4095 bytes can be accommodated. |
| 824 | * If the offset is larger than 4095 bytes, a compile-time error will |
| 825 | * be generated in __kfree_rcu(). If this error is triggered, you can |
| 826 | * either fall back to use of call_rcu() or rearrange the structure to |
| 827 | * position the rcu_head structure into the first 4096 bytes. |
| 828 | * |
| 829 | * Note that the allowable offset might decrease in the future, for example, |
| 830 | * to allow something like kmem_cache_free_rcu(). |
| 831 | * |
| 832 | * The BUILD_BUG_ON check must not involve any function calls, hence the |
| 833 | * checks are done in macros here. |
| 834 | */ |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 835 | #define kfree_rcu(ptr, rhf) \ |
| 836 | do { \ |
| 837 | typeof (ptr) ___p = (ptr); \ |
| 838 | \ |
| 839 | if (___p) \ |
| 840 | __kfree_rcu(&((___p)->rhf), offsetof(typeof(*(ptr)), rhf)); \ |
| 841 | } while (0) |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 842 | |
| 843 | /* |
| 844 | * Place this after a lock-acquisition primitive to guarantee that |
| 845 | * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies |
| 846 | * if the UNLOCK and LOCK are executed by the same CPU or if the |
| 847 | * UNLOCK and LOCK operate on the same lock variable. |
| 848 | */ |
| 849 | #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE |
| 850 | #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */ |
| 851 | #else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ |
| 852 | #define smp_mb__after_unlock_lock() do { } while (0) |
| 853 | #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ |
| 854 | |
| 855 | |
David Brazdil | 0f672f6 | 2019-12-10 10:32:29 +0000 | [diff] [blame] | 856 | /* Has the specified rcu_head structure been handed to call_rcu()? */ |
| 857 | |
| 858 | /** |
| 859 | * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu() |
| 860 | * @rhp: The rcu_head structure to initialize. |
| 861 | * |
| 862 | * If you intend to invoke rcu_head_after_call_rcu() to test whether a |
| 863 | * given rcu_head structure has already been passed to call_rcu(), then |
| 864 | * you must also invoke this rcu_head_init() function on it just after |
| 865 | * allocating that structure. Calls to this function must not race with |
| 866 | * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation. |
| 867 | */ |
| 868 | static inline void rcu_head_init(struct rcu_head *rhp) |
| 869 | { |
| 870 | rhp->func = (rcu_callback_t)~0L; |
| 871 | } |
| 872 | |
| 873 | /** |
| 874 | * rcu_head_after_call_rcu - Has this rcu_head been passed to call_rcu()? |
| 875 | * @rhp: The rcu_head structure to test. |
| 876 | * @f: The function passed to call_rcu() along with @rhp. |
| 877 | * |
| 878 | * Returns @true if the @rhp has been passed to call_rcu() with @func, |
| 879 | * and @false otherwise. Emits a warning in any other case, including |
| 880 | * the case where @rhp has already been invoked after a grace period. |
| 881 | * Calls to this function must not race with callback invocation. One way |
| 882 | * to avoid such races is to enclose the call to rcu_head_after_call_rcu() |
| 883 | * in an RCU read-side critical section that includes a read-side fetch |
| 884 | * of the pointer to the structure containing @rhp. |
| 885 | */ |
| 886 | static inline bool |
| 887 | rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f) |
| 888 | { |
| 889 | rcu_callback_t func = READ_ONCE(rhp->func); |
| 890 | |
| 891 | if (func == f) |
| 892 | return true; |
| 893 | WARN_ON_ONCE(func != (rcu_callback_t)~0L); |
| 894 | return false; |
| 895 | } |
| 896 | |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 897 | #endif /* __LINUX_RCUPDATE_H */ |